Module:Set
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Documentation for this module may be created at Module:Set/doc
-- <nowiki> -------------------------------------------------------------------------------- -- Library for building and manipulating sets. -- -- @author [[User:DarthKitty]] -- @version 0.5.0 -- -- @TODO Consider adding a `clone` function, since `mw.clone` doesn't work. -- @TODO Consider using `pairs` internally, to cut down on (en|de)coding. -- @TODO Consider using `Module::Inspect` for `tostring`. -------------------------------------------------------------------------------- local p = {} -------------------------------------------------------------------------------- -- Pass-by-reference placeholders for values that cannot be used as table keys. -- We use functions instead of tables, since the latter are mutable. -------------------------------------------------------------------------------- local placeholders = { ["nil"] = function () end, ["NaN"] = function () end, } -------------------------------------------------------------------------------- -- An ephemeron table is the closest approximation of JavaScript's `WeakMap` -- object, and can be used to store private, per-instance data. This is more -- efficient than using a closure, since it doesn't rebuild the whole -- metatable for every instance. -- -- @see <http://fitzgeraldnick.com/2014/01/13/hiding-implementation-details-with-e6-weakmaps.html> -------------------------------------------------------------------------------- local internals = setmetatable({}, { __mode = "k", __index = function () error("This set has not been initialized correctly. Please use `Module:Set.init` to construct new instances") end, }) -------------------------------------------------------------------------------- -- Metatable for set instances. Provides method syntax and overloaded operators -- for convenience. -------------------------------------------------------------------------------- local Set = { __index = {}, __newindex = function () error("cannot change a protected table") end, __metatable = false, } -------------------------------------------------------------------------------- -- Wraps a given value for use as a table key. -- -- @param {*} value -- The value to wrap. -- @returns {*} -- The wrapped value. -------------------------------------------------------------------------------- local function encode(value) -- Per IEEE 754, NaN is the only value which does not equal itself. Tables -- cannot generate false-positives, since the `__eq` metamethod is not -- called if the values being compared are primitively equal. local isNaN = value ~= value if value == nil then return placeholders["nil"] elseif isNaN then return placeholders["NaN"] else return value end end -------------------------------------------------------------------------------- -- Unwraps a given value after being used as a table key. -- -- @param {*} value -- The value to unwrap. -- @returns {*} -- The unwrapped value. -------------------------------------------------------------------------------- local function decode(value) if value == placeholders["nil"] then return nil elseif value == placeholders["NaN"] then return 0 / 0 -- There's no `NaN` literal. else return value end end -------------------------------------------------------------------------------- -- Constructs a set instance. -- -- @returns {table} -- A new set. -------------------------------------------------------------------------------- local function init() local set = setmetatable({}, Set) internals[set] = { elements = {}, size = 0, prevElement = nil, } return set end p.init = init -------------------------------------------------------------------------------- -- Checks if a value is a set, as defined by this library. -- -- @param {*} value -- The value to check. -- @returns {boolean} -- Whether the value is a set. -------------------------------------------------------------------------------- local function is(value) return (pcall(function () return internals[value] end)) end p.is = is -------------------------------------------------------------------------------- -- Fetches the number of elements in a set. -- -- @see [[wikipedia:Cardinality]] -- -- @param {table} set -- A set. -- @returns {number} -- The number of elements in the set. -------------------------------------------------------------------------------- local function size(set) if not is(set) then error("bad argument #1 to 'Module:Set.size' (set expected, got " .. type(set) .. ")", 2) end return internals[set].size end p.size = size Set.__index.size = size -------------------------------------------------------------------------------- -- Checks if a set has a particular element. -- -- @param {table} set -- The set to search. -- @param {*} element -- The element to search for. -- @returns {boolean} -- Whether the set contains the element. -------------------------------------------------------------------------------- local function contains(set, element) if not is(set) then error("bad argument #1 to 'Module:Set.contains' (set expected, got " .. type(set) .. ")", 2) end return not not internals[set].elements[encode(element)] end p.contains = contains Set.__index.contains = contains -------------------------------------------------------------------------------- -- Fetches the "next" element in a set, wrapping around to the "beginning" if -- the "previous" was also the "last". Since sets are unordered, the meaning of -- those terms is determined by the built-in `next` function. -- -- This method is provided as a workaround for Lua's horribly-designed iterator -- "protocol". Iterators use `nil` to signal the end of a sequence, but since -- this "class" accepts `nil` elements, it is impossible to write an iterator -- which will always loop over every element. Furthermore, because sets are not -- ordered, such an iterator would stop at an arbitrary position. -- -- Instead, combining this method with `Module:Set.size` allows users to loop over -- a set numerically, much like the `"n"` field trick utilized for sequential -- tables with holes. -- -- @param {table} set -- A set. -- @returns {*} -- An element in the set. -------------------------------------------------------------------------------- local function nextElement(set) if not is(set) then error("bad argument #1 to 'Module:Set.nextElement' (set expected, got " .. type(set) .. ")", 2) end local element = next(internals[set].elements, internals[set].prevElement) -- If we've reached the end of the set, start over from the beginning. if element == nil then element = next(internals[set].elements, element) end -- Advance the pointer. internals[set].prevElement = element return decode(element) end p.nextElement = nextElement Set.__index.nextElement = nextElement -------------------------------------------------------------------------------- -- Adds one element to a set. -- -- @param {table} set -- The set to add to. -- @param {*} element -- The element to add. -- @returns {table} -- The same set instance. -------------------------------------------------------------------------------- local function add(set, element) if not is(set) then error("bad argument #1 to 'Module:Set.add' (set expected, got " .. type(set) .. ")", 2) end if not contains(set, element) then internals[set].elements[encode(element)] = true internals[set].size = internals[set].size + 1 end return set end p.add = add Set.__index.add = add -------------------------------------------------------------------------------- -- Removes one element from a set. -- -- @param {table} set -- The set to remove from. -- @param {*} element -- The element to remove. -- @returns {table} -- The same set instance. -------------------------------------------------------------------------------- local function remove(set, element) if not is(set) then error("bad argument #1 to 'Module:Set.remove' (set expected, got " .. type(set) .. ")", 2) end if contains(set, element) then internals[set].elements[encode(element)] = nil internals[set].size = internals[set].size - 1 end return set end p.remove = remove Set.__index.remove = remove -------------------------------------------------------------------------------- -- Removes all elements from a set. -- -- @param {table} set -- The set to remove from. -- @returns {table} -- The same set instance. -------------------------------------------------------------------------------- local function clear(set) if not is(set) then error("bad argument #1 to 'Module:Set.clear' (set expected, got " .. type(set) .. ")", 2) end for i = 1, size(set) do remove(set, nextElement(set)) end return set end p.clear = clear Set.__index.clear = clear -------------------------------------------------------------------------------- -- Constructs a set with one or more elements. -- -- @param {...*} ... -- The elements to add. -- @returns {table} -- The set. -------------------------------------------------------------------------------- local function of(...) local set = init() for i = 1, select("#", ...) do add(set, select(i, ...)) end return set end p.of = of -------------------------------------------------------------------------------- -- Constructs a set from a the key-value pairs of a table, adding keys that -- correspond to "truthy" values and ignoring the rest. -- -- @param {table} tbl -- The table to iterate over. -- @returns {table} -- The set. -------------------------------------------------------------------------------- local function fromPairs(tbl) local typ = type(tbl) if typ ~= "table" then error("bad argument #1 to 'Module:Set.fromPairs' (table expected, got " .. typ .. ")", 2) end local set = init() for key, value in pairs(tbl) do if value then add(set, key) end end return set end p.fromPairs = fromPairs -------------------------------------------------------------------------------- -- Builds a new set from two existing ones, where each element of the former is -- also an element of both of the latter. -- -- @see [[wikipedia:Intersection (set theory)]] -- -- @param {table} oldSet1 -- A set. -- @param {table} oldSet2 -- A set. -- @returns {table} -- A new set. -------------------------------------------------------------------------------- local function intersection(oldSet1, oldSet2) if not is(oldSet1) then error("bad argument #1 to 'Module:Set.intersection' (set expected, got " .. type(oldSet1) .. ")", 2) end if not is(oldSet1) then error("bad argument #2 to 'Module:Set.intersection' (set expected, got " .. type(oldSet2) .. ")", 2) end local newSet = init() for i = 1, size(oldSet1) do local element = nextElement(oldSet1) if contains(oldSet2, element) then add(newSet, element) end end return newSet end p.intersection = intersection Set.__index.intersection = intersection Set.__mul = intersection -------------------------------------------------------------------------------- -- Builds a new set from two existing ones, where each element of the former is -- also an element of either of the latter. -- -- @see [[wikipedia:Union (set theory)]] -- -- @param {table} oldSet1 -- A set. -- @param {table} oldSet2 -- A set. -- @returns {table} -- A new set. -------------------------------------------------------------------------------- local function union(oldSet1, oldSet2) if not is(oldSet1) then error("bad argument #1 to 'Module:Set.union' (set expected, got " .. type(oldSet1) .. ")", 2) end if not is(oldSet2) then error("bad argument #2 to 'Module:Set.union' (set expected, got " .. type(oldSet2) .. ")", 2) end local newSet = init() for _, oldSet in ipairs{oldSet1, oldSet2} do for i = 1, size(oldSet) do add(newSet, nextElement(oldSet)) end end return newSet end p.union = union Set.__index.union = union Set.__add = union -------------------------------------------------------------------------------- -- Builds a new set from two existing ones, where each element of the former is -- also an element of the first of the latter, but not the second. -- -- @see [[wikipedia:Complement (set theory)#Relative complement]] -- -- @param {table} oldSet1 -- A set. -- @param {table} oldSet2 -- A set. -- @returns {table} -- A new set. -------------------------------------------------------------------------------- local function difference(oldSet1, oldSet2) if not is(oldSet1) then error("bad argument #1 to 'Module:Set.difference' (set expected, got " .. type(oldSet1) .. ")", 2) end if not is(oldSet1) then error("bad argument #2 to 'Module:Set.difference' (set expected, got " .. type(oldSet2) .. ")", 2) end local newSet = init() for i = 1, size(oldSet1) do local element = nextElement(oldSet1) if not contains(oldSet2, element) then add(newSet, element) end end return newSet end p.difference = difference Set.__index.difference = difference Set.__sub = difference -------------------------------------------------------------------------------- -- Builds a new set from two existing ones, where each element of the former is -- also an element of one of the latter, but not both. -- -- @see [[wikipedia:Symmetric difference]] -- -- @param {table} oldSet1 -- A set. -- @param {table} oldSet2 -- A set. -- @returns {table} -- A new set. -------------------------------------------------------------------------------- local function symmetricDifference(oldSet1, oldSet2) if not is(oldSet1) then error("bad argument #1 to 'Module:Set.symmetricDifference' (set expected, got " .. type(oldSet1) .. ")", 2) end if not is(oldSet1) then error("bad argument #2 to 'Module:Set.symmetricDifference' (set expected, got " .. type(oldSet2) .. ")", 2) end local newSet = init() for _, oldSet in ipairs{oldSet1, oldSet2} do for i = 1, size(oldSet) do local element = nextElement() if contains(newSet, element) then remove(newSet, element) else add(newSet, element) end end end return newSet end p.symmetricDifference = symmetricDifference Set.__index.symmetricDifference = symmetricDifference Set.__pow = symmetricDifference -------------------------------------------------------------------------------- -- Checks if two sets have no elements in common. -- -- @see [[wikipedia:Disjoint sets]] -- -- @param {table} set1 -- A set. -- @param {table} set2 -- A set. -- @returns {boolean} -- Whether the two sets have no elements in common. -------------------------------------------------------------------------------- local function isDisjointFrom(set1, set2) if not is(set1) then error("bad argument #1 to 'Module:Set.isDisjointFrom' (set expected, got " .. type(set1) .. ")", 2) end if not is(set1) then error("bad argument #2 to 'Module:Set.isDisjointFrom' (set expected, got " .. type(set2) .. ")", 2) end for i = 1, size(set1) do if contains(set2, nextElement(set1)) then return false end end return true end p.isDisjointFrom = isDisjointFrom Set.__index.isDisjointFrom = isDisjointFrom -------------------------------------------------------------------------------- -- Checks if every element of one set is also an element of another. -- -- @see [[wikipedia:Subset]] -- -- @param {table} set1 -- A set. -- @param {table} set2 -- A set. -- @returns {boolean} -- Whether every element of the first set is also an element of the second. -------------------------------------------------------------------------------- local function isSubsetOf(set1, set2) if not is(set1) then error("bad argument #1 to 'Module:Set.isSubsetOf' (set expected, got " .. type(set1) .. ")", 2) end if not is(set1) then error("bad argument #2 to 'Module:Set.isSubsetOf' (set expected, got " .. type(set2) .. ")", 2) end for i = 1, size(set1) do if not contains(set2, nextElement(set1)) then return false end end return true end p.isSubsetOf = isSubsetOf Set.__index.isSubsetOf = isSubsetOf Set.__le = isSubsetOf -------------------------------------------------------------------------------- -- Checks if every element of one set is also an element of another, but not the -- inverse. -- -- @see [[wikipedia:Subset]] -- -- @param {table} set1 -- A set. -- @param {table} set2 -- A set. -- @returns {boolean} -- Whether every element of the first set is also an element of the second, -- but not the inverse. -------------------------------------------------------------------------------- local function isProperSubsetOf(set1, set2) if not is(set1) then error("bad argument #1 to 'Module:Set.isProperSubsetOf' (set expected, got " .. type(set1) .. ")", 2) end if not is(set1) then error("bad argument #2 to 'Module:Set.isProperSubsetOf' (set expected, got " .. type(set2) .. ")", 2) end return size(set1) < size(set2) and isSubsetOf(set1, set2) end p.isProperSubsetOf = isProperSubsetOf Set.__index.isProperSubsetOf = isProperSubsetOf Set.__lt = isProperSubsetOf -------------------------------------------------------------------------------- -- Checks if every element of one set is also an element of another, and vice -- versa. -- -- @param {table} set1 -- A set. -- @param {table} set2 -- A set. -- @returns {boolean} -- Whether every element of the first set is also an element of the second, -- and vice versa. -------------------------------------------------------------------------------- local function equals(set1, set2) if not is(set1) then error("bad argument #1 to 'Module:Set.equals' (set expected, got " .. type(set1) .. ")", 2) end if not is(set1) then error("bad argument #2 to 'Module:Set.equals' (set expected, got " .. type(set2) .. ")", 2) end return size(set1) == size(set2) and isSubsetOf(set1, set2) end p.equals = equals Set.__index.equals = equals Set.__eq = equals -------------------------------------------------------------------------------- -- Generates a string representation of a set. -- -- @param {table} set -- A set. -- @returns {string} -- A string representation of the set. -------------------------------------------------------------------------------- local function tostring_(set) local tmp = {} for i = 1, size(set) do tmp[i] = tostring(nextElement(set)) end return "Set { " .. table.concat(tmp, ", ") .. " }" end Set.__tostring = tostring_ -- Makes it slightly more convenient to construct set instances, by allowing -- users to omit ".of". return setmetatable(p, { __call = function (self, ...) return self.of(...) end, })